So-called “gel” cards or “bead” cassettes are now commonly used, for example, in the field of immunohematological testing as test elements for blood typing, blood grouping and/or the detection of certain antigens or antibodies. These test elements are commonly defined by a flat planar substrate having a plurality of transparent microtubes or columns that define test chambers. A predetermined quantity of inert bead or gel material is added to each of the microtubes. This inert material may be coated with an antibody or an antigen or provided with a carrier-bound antibody or antigen or with specific reagents. Typically, a foil wrap is used to cover the top of the card or cassette, thereby sealing the contents of each microtube until the time of test. The foil wrap is pierceable or otherwise removed to enable aliquots of patient sample and/or reagents to be added to each of the microtubes, either manually or in an automated apparatus. The sample is incubated and then mixed into the contents of the test chambers by centrifugation. During centrifugation, red blood cells (RBCs) in each reaction chamber are pulled into the gel column. Agglutinated RBCs are too large to pass through the gel matrix, depending on the size of the agglutinates, while unagglutinized RBCs will pass easily through the gel and pellet at the bottom of the chamber.
A grading system is used with regard to a resulting agglutination reaction with regard to RBC agglutinates that are trapped anywhere in the gel column. Positive reactions can be graded from 0 to 4+. More specifically, a 4+ reaction is indicated by a solid band of RBCs on top of the gel. A 3+ reaction displays agglutinated RBCs in the upper half of the gel column. A 2+ column is characterized by RBC agglutinates dispersed throughout the length of the column. A 1+ column is indicated by RBC agglutinates mainly in the lower half of the gel column with some agglutinated RBCs being pelleted at the bottom of the column. Negative (0) reactions are characterized by a pellet of RBCs on the bottom of the microtube with no agglutinates along the length of the column. In the course of testing, the resulting reaction can be highly positive; that is, all or most of the formed agglutinate is disposed above the inert material layer, or highly negative; that is, in which no agglutination results and all of the cells is located at the bottom of the microtube as a pellet. Gradients of these reactions are also produced wherein formed agglutinate can be distributed anywhere throughout the gel/bead matrix and wherein this distribution must be graded as being either highly or weakly positive.
The grading of agglutination reactions using immunodiagnostic test cards, such as those manufactured by DiaMed, Inc. and Micro-Typing Systems, Inc., among others, is somewhat difficult, for agglutination reactions, for example that are not highly positive or highly negative. Among the most difficult to grade are those reactions between a 4+ and a 3+ reaction and between a 1+ and a negative (0) reaction. Ultimately, such determination becomes highly user-dependent especially when the test cards or cassettes are read manually, making the process extremely subjective as to the position of agglutinates in the column, and requiring users who have significant experience perform the reading operation in order to obtain consistent results. In addition and because the card or cassette surface is typically relatively smooth throughout, it is often difficult for image processing algorithms of automated apparatus to accurately locate the exact position of the column(s) in the field of view. Exemplary image processing algorithms are described, for example, in EP Patent 0 637 744 to Shen et al. This perceived difficulty drives additional cost into the design of a suitable illumination system. Having an incorrect determination can produce dire or fatal consequences; for example in instances for determining proper blood samples for transfusion.
The manufacturing of test elements as described above is also dependent upon adding the proper amount of inert material into each of the microtubes. Though this manufacturing process can be automated, errors can still result. For example, a dispensing mechanism can be improperly positioned relative to the test element or tolerance buildup issues may have occurred in the manufacture of a card or cassette, requiring in-process manufacturing checks for fill volume and label placement. If an improper amount of inert material is provided in any of the microtubes, the results as graded from the resulting agglutination reaction may not be accurate. For those reasons, among others, it is desirable to improve the design of immunodiagnostic test cards and cassettes.